Teeth are often polished with the aid of polishing nozzles that blow a polishing mixture of air and powder against the tooth to be polished. The powder is most often bicarbonate. Another gas can be used instead of air. Jets of water that form a curtain around the powder/air suspension are also sprayed onto the tooth to prevent dusting.
The principle developed in accordance with the invention is not restricted solely to polishing operations, but can also be applied with other types of powder, such as Al2O3 for instance, to abrade a tooth in scaling an outer surface of the tooth, or can be applied instead of conventional drilling. A small polishing and drilling nozzle may, of course, also be used in contexts other than with teeth, for instance in connection with manicures, the production of jewellery, and the like.
A number of different systems in which the aforesaid principle is used are known to the art. For instance, U.S. Pat. Nos. 3,972,123, 4,174,571 and 4,696,644 teach a tooth-polishing nozzle which includes mutually concentric tubes of which the centre tube conveying the powder/air suspension projects in relation to the outermost tube, wherein water is conveyed in a channel defined between both tubes. U.S. Pat. No. 4,412,402 describes a more functional design where the centremost tube carrying the powder/air suspension is withdrawn in relation to the water-conveying outer tube. In addition, the faster flowing powder/air suspension is able to entrain at least a part of the much slower water flow, up to the orifice of the polishing nozzle.
One problem with earlier designs is that the powder/air suspension has a rate of flow of about 15-20 ml/min., while only a total flow of water of 5-15 ml/min. can be achieved. It will be noted that the lowest possible water flow is desired, so that the patient will not feel that he is drowning in water and so that not too much water will be applied to the surface of the tooth being polished. Powder particles will then be deposited in the water instead of on the tooth. This means that the air velocity vair will be about 1000 to 1500 times the water velocity vwater. Although it is true that some water will be entrained by the air in the device described in U.S. Pat. No. 4,412,402 in particular, the effect achieved therewith is in no way satisfactory. Furthermore, there is a significant imbalance between ejection of the powder/air suspension and the water, due to the different velocities, which gives rise to turbulence and vigorous mixing between the flows.
One object of the invention is to provide a surface treatment nozzle which functions to eject powder/gas and a liquid-containing protective curtain, where said ejections have the least possible effect on one another.
Another object of the invention is to provide a surface treatment nozzle that ejects powder/gas and a liquid-containing protective curtain where but small turbulence is obtained between the different flows.
Another object of the invention is to provide a surface treatment nozzle that includes but few separate parts and is readily manufactured.
The invention thus relates to an improved surface treatment nozzle for generating a surface treatment jet comprising a suspension of surface treatment material and gas and a liquid-containing surrounding jet for preventing xe2x80x9cdustingxe2x80x9d, wherein the surface treatment jet has a greater velocity than the velocity of solely liquid, wherein the surface treatment jet is conveyed in an inner tube and the liquid in a channel located between said inner tube and a tube that surrounds the inner tube concentrically. According to the invention, there is provided a mixing arrangement for mixing liquid with gas upstream of the nozzle outlet and imparting to the liquid/gas suspension a velocity of the same order of magnitude as the velocity of the surface treatment jet at said outlet.
The mixing arrangement will preferably include an internal outlet from the liquid conveying channel and discharge means for delivering part of the gas in the surface treatment jet, as gas for producing the gas/liquid mixture in an amount such as to impart the desired velocity thereto. The mixing arrangement may include an expansion channel for the liquid and gas mixture externally of the discharge means. The mixing arrangement will preferably include an at least internal constriction of the inner tube downstream of the discharge means.
The inner tube that conveys the surface treatment material/gas suspension may be circular at least at the nozzle orifice and have a diameter which provides space for a surrounding flow of the liquid/gas mixture through cavities around the orifice of the inner tube. The cavities around the orifice of the inner tube may comprise a ring of drilled holes or a central irregular hole that includes wall parts which provide internal support for the orifice of said inner tube when said tube is inserted in the central hole.
The inner tube (13; 31) conveying the suspension of surface treatment material and gas may have a polygonal orifice (28), e.g., an orifice with three corners, at least up to the nozzle orifice, and the nozzle orifice may have a central round hole (27) with a diameter adapted as a corner support and to provide space for a surrounding flow of liquid and gas mixture through said cavities around the orifice (28) of the inner tube. The sizes and forms of the discharge means, the expansion channel, the inner constriction and the cavities through which the liquid/gas mixture exits should be balanced in relation to each other such as to achieve the best possible similarity between the respective velocities of the suspension of surface treatment material and gas and the mixture of liquid and gas. The gas may be air and the surface treatment material may be a polishing material, for instance bicarbonate, or an abrasive material, for instance Al2O3.
Because the velocities of both ejected flows lie in the same order of magnitude, there is practically no turbulence between the flows at the outlet orifice of the surface treatment nozzle. Reduced turbulence results in improved efficiency and also in small inter-mixing between the flow areas.